diff --git a/README.md b/README.md
index 93f2574..f4c8d11 100644
--- a/README.md
+++ b/README.md
@@ -108,6 +108,24 @@ fmt.Printf("Fetching the following IDs from %s: %q", args.Database, args.IDs)
 Fetching the following IDs from foo: [1 2 3]
 ```
 
+### Custom validation
+```go
+var args struct {
+	Foo string
+	Bar string
+}
+p := arg.MustParse(&args)
+if args.Foo == "" && args.Bar == "" {
+	p.Fail("you must provide one of --foo and --bar")
+}
+```
+
+```shell
+./example
+usage: samples [--foo FOO] [--bar BAR]
+error: you must provide one of --foo and --bar
+```
+
 ### Installation
 
 ```shell
diff --git a/parse.go b/parse.go
index b6eae4e..219a947 100644
--- a/parse.go
+++ b/parse.go
@@ -26,7 +26,7 @@ type spec struct {
 var ErrHelp = errors.New("help requested by user")
 
 // MustParse processes command line arguments and exits upon failure
-func MustParse(dest ...interface{}) {
+func MustParse(dest ...interface{}) *Parser {
 	p, err := NewParser(dest...)
 	if err != nil {
 		fmt.Println(err)
@@ -40,6 +40,7 @@ func MustParse(dest ...interface{}) {
 	if err != nil {
 		p.Fail(err.Error())
 	}
+	return p
 }
 
 // Parse processes command line arguments and stores them in dest
diff --git a/parse_test.go b/parse_test.go
index eb6080c..7fca76a 100644
--- a/parse_test.go
+++ b/parse_test.go
@@ -353,6 +353,7 @@ func TestMustParse(t *testing.T) {
 		Foo string
 	}
 	os.Args = []string{"example", "--foo", "bar"}
-	MustParse(&args)
+	parser := MustParse(&args)
 	assert.Equal(t, "bar", args.Foo)
+	assert.NotNil(t, parser)
 }